it's not that easy, unfortunately. usually, the faster developing specimens can be suspected to be male after a long period of watching them and comparing their growth rate with their sac mates. but this is not true for all specimen.
growth rates and thus molting frequency depends on temperature, humidity, food, willingness to feed, genetics, health,... and a lot of other factors i forgot or we know nothing about.
as a rule, if you raise specimen from the same sac, most of the males will mature before many of the females do. this doesn't necessarily mean that your slow growing specimen is a female and the fast growing one is a male, though. the only secure way to tell is an exuvium...
Not really true. I am pretty sure that males have a fewer number of molts they can have in their lifetimes. You figure lets say for example females need 9 molts to hit 6". Figurativaly speaking,males of the same species could be mature in 6 molts.
So yes food intake and temps and all that play a factor on growth rates, but not the number of actual molts a T needs male or female to mature.